Slurry Cutoff Walls: Applications in the Control of Hazardous Wastes

Slurry cutoff walls are nonstructural barriers constructed to intercept and impede the flow of fluids underground. There are two basic types of slurry cutoff walls, soil-bentonite (SB) and cement-bentonite (CB). Depending on the nature of the project, either method may have some technical or economic advantage over the other. In both cases, a narrow trench is excavated into the ground using a backhoe or other more specialized equipment. The trench is prevented from collapsing by keeping it full at all times with bentonite slurry similar to drilling mud. In the case of SB walls, the trench is subsequently backfilled with a mixture of soil and bentonite slurry that forms the permanent impervious cutoff wall. With the CB method, cement is added to the slurry, which later sets up, forming the permanent seepage barrier.

Slurry cutoff walls are being used in an increasing variety of applications to provide a barrier to the lateral underground flow of various fluids. Principal applications are site dewatering, underground pollution control, and seepage barriers under dams. In this paper, case studies are used to provide examples of recent applications in the control of leaching hazardous wastes.

Projects cited include:

1. Containment of oil seeping through a reservoir abutment.

2. Cleanup of a polychlorinated biphenyl (PCB) contaminated site.

3. Containment of leachates and methane gas migration from a sanitary landfill site.

4. Cleanup of a site with spilled phenols.

All of the examples were selected because of the unusual conditions under which they were constructed or because of the dramatic evidence of results.